The present invention relates to intraocular lenses and to fixation member assemblies for use in such lenses. More particularly, the present invention relates to such intraocular lenses and fixation member assemblies which provide enhanced bonding strength between the components of the lenses and assemblies and/or have enhanced biocompatibility.
The use of intraocular lenses (IOLs) to improve vision and/or to replace damaged or diseased natural lenses in human eyes, particularly natural lenses impaired by cataracts, has attained wide acceptance. Accordingly, a variety of IOLs has been developed for surgical implantation in the posterior or anterior chambers of the eye according to a patient's needs.
Known IOLs comprise an optical lens portion or optic which includes an optical zone, and one or more, for example two, supporting structures, called fixation members, for example, loops or haptics, for contacting eye tissue to fix or hold the IOL in the proper position after implantation. The optic may comprise a soft, resilient material, such as any of a variety of flexible elastomers, or a relatively hard or rigid material such as, for example, polymethylmethacrylate (PMMA). The fixation members may comprise a filament constructed of resilient metal or polymeric substance, such as polymethylmethacrylate (PMMA) or polypropylene.
Each of the filament fixation members is preferably flexible to reduce trauma to sensitive eye structures and to be yielding during insertion of the IOL. In addition, filament fixation members generally have a memory retaining capability, e.g., springiness, so that after implantation of an associated IOL, the filament fixation members automatically tend to return to their normal orientations.
As an alternative to filament fixation members, some IOLs are provided with footplate-type fixation members. These footplates generally extend radially outwardly from the optic (for example, in the plane of the optic) and terminate in rounded or blunted ends configured for placement in an eye chamber. The materials for such footplates have included soft materials, for example, 2-hydroxyethyl methacrylate or silicone.
Although the filament fixation members are preferred over the footplate-type fixation members for several reasons, certain difficulties remain. For example, filament fixation members and soft or deformable optics tend to be formed from dissimilar materials which do not ordinarily chemically bond together. As a result, filament fixation members have been designed having a variety of attachment end configurations or structures, e.g., anchor structures for providing a physical interlock between the haptic and optic. Polypropylene fixation members, for example, have heretofore been secured into silicone polymer-based optics by means of a mechanical lock. This lock may comprise a small loop or other anchor formed at the attachment end of the haptic through and/or around which the silicone-based optic precursor material is poured or molded and then cured. Christ et al U.S. Pat. No. 4,790,846 discloses the molding of an optic around a fixation members having a small loop or other anchor to effect a secure fixation members connection.
Christ et al U.S. Pat. No. 4,790,846 further discloses a method for making an IOL in which a region of an elongated filament haptic has a different configuration, e.g., a bulbous enlargement, which cooperates with the optic of the IOL to form a mechanical interlock between this different configuration and the optic and to attach to the optic. If desired, the bulbous enlargement may have its outer surface roughened to improve adhesion of the material of the optic.
Koziol, et al U.S. Pat. Nos. 4,615,702 and 4,702,865 disclose a one-piece haptic structure which comprises an annular loop portion for surrounding the optical pathway or zone through the optic, and having a pair of mounting arms extending radially outwardly from the loop. The loop is embedded within the optic during molding and polymerization of the optic to provide a mechanical interfit. However, the loop can be aesthetically displeasing, and can interfere with peripheral sight through the optic. In addition, the optic is difficult to fold (for the purpose of placing the lens in the eye) without cracking or breaking the loop. Also, due to the lack of chemical interaction between the haptic and the optic, gaps can form at the haptic-optic interface which further impair the optical integrity of the optic.
Kaplan et al U.S. Pat. No. 4,668,446 discloses an alternative method of attaching haptics to the optic of an IOL wherein an enlarged attachment end of the haptic is secured in the optic. This method involves an ethanol induced swelling of a bore hole in the optic, insertion of the enlarged end of the haptic into this bore hole, and removal of the ethanol to shrink the bore hole around the enlarged end of the haptic, thereby producing a mechanical anchoring.
One additional disadvantage of certain fixation members is that they may not be suitably biocompatible, for example, with the ocular tissue which is present when the IOL is in use. The use of biocompatible coatings on such fixation members has an additional disadvantage that such coatings tend to disassociate from the base fixation member.
Freeman U.S. Pat. No. 4,718,905 discloses an IOL including an optic composed of PMMA and haptic loops fashioned from polypropylene strand material. Each haptic strand is coated, using ion beam implantation, with a biocompatible protective ion coating of nitrogen, carbon, silicon or aluminum to protect it from the bioerodable effects of ocular tissue. This patent does not teach, or even suggest, other protective coatings or enhanced haptic-optic bonding. Also, there is no teaching that the haptic loop is subjected to ion beam implantation prior to being secured to the optic.
Notwithstanding these known structures and methods, there remains a need for a method of efficiently and effectively providing structurally durable, biocompatible fixation members which can be secured to the optic of an IOL, preferably without the use of mechanical interlocking structures, so that the fixation member-optic bond is sufficient to resist detachment of the fixation member under normal implantation and wear conditions.
The use of gas plasmas to activate and/or add functional groups to surfaces of fibers is known. For example, see: "Plasma Treatment Effect in the Surface Energy of Carbon and Carbon Fibers", J. B. Donnet, et al, Carbon, Vol. 24, No. 6 pp 757-770 (1986); and "Introduction of Functional Groups Onto Carbon Electrode Via Treatment With Radio-Frequency Plasma", J. F. Evans, et al, Analytical Chemistry, Vol. 51, No. 3, pp 358-365 (1979). Further, Goan U.S. Pat. No. 3,776,829 discloses reacting carbon fibers with ammonia plasma to form amino groups on the fiber surfaces. The amine groups act as cross linking agents for an epoxy resin matrix in the preparation of sized fibers, pre-impregnated tapes, and compositions containing the fibers. None of these documents teach or suggest anything regarding IOLs, let alone enhancing the bondability between fixation members and optics of IOLs.